Untangling the determinants of selective electron transfer between nitrogen fixation and aromatic compound degradation reveals the importance of the electron donor-ferredoxin interactions in determining redox flux II

Recent evidence suggests that some ferredoxins are specific to one electron transfer pathway while others interact broadly, but the determinants of this specificity remain unclear. Existing literature highlights several mechanisms in controlling Fd specificity including the regulation of Fd expression, tuning Fe-S cluster properties, and structural compatibility between Fds and their redox partners, but it is unclear which properties are practically important for re-wiring electron flow.

In this study, we use the model phototrophic diazotroph, Rhodopseudomonas palustris to identify which properties needed to change to allow the Fd from anaerobic aromatic compound degradation (BadB) to support nitrogen fixation. We found that BadB does not natively support nitrogen fixation although it is highly over-expressed during growth on aromatic compounds in nitrogen fixing conditions. Seemingly inconsistent with our growth data, in silico docking studies suggested BadB could form a productive electron transfer complex with nitrogenase without any structural changes, hinting that some other property prevented BadB from reacting with nitrogenase.